The present invention relates to circuitry for controlling the directivity of an adaptive antenna and more particularly to directivity control circuitry for an adaptive antenna included in a CDMA (Code Division Multiple Access) mobile communication system.
It is a common practice with an adaptive antenna applied to mobile communication to provide a base station, rather than a mobile station, with the function of the adaptive antenna. Specifically, the adaptive antenna is more practical when installed in a base station than when installed in a mobile station from the apparatus scale standpoint. Further, as for the directivity control of the adaptive antenna, the adaptability of the control can be improved if the result of the previous control is fed back for generating the next control parameter. Therefore, installing the adaptive antenna in the receiving side is simpler than installing it in the transmitting side. For these reasons, the adaptive antenna is often adopted for directivity control on an uplink.
The above conventional scheme allows the uplink capacity to be increased because of the effect of the adaptive antenna, but cannot improve the downlink capacity at all. Moreover, the entire system cannot make the most of the effect of the adaptive antenna because the downlink capacity is the bottleneck.
In light of the above, there has been proposed to use a number of fixed directivity patterns for a downlink (multisector scheme) or to estimate the down link propagation characteristic on the basis of the parameter of uplink directivity control and then determine a directivity control parameter for the downlink.
However, it has been customary with radio communication to assign a particular frequency to each of the uplink and downlink in order to avoid interference. Therefore, the uplink and downlink do not always have the same propagation characteristic. Should the directivity parameter of the uplink be directly used as a directivity parameter for the down link, a difference would occur in propagation characteristic. Specifically, should the directivity of the downlink be sharp, it would fail to cover the location of the mobile station and would cause a signal to be sent in an unexpected direction. For this reason, it has heretofore been impractical to render the downlink directivity as sharp as the uplink directivity. That is, directivity broad enough to accommodate errors has heretofore been assigned to the downlink. This aggravates interference as to the other mobile stations and thereby limits the improvement in capacity, compared to the uplink.
Technologies relating to the present invention are disclosed in, e.g.. Japanese Patent Laid-Open Publication Nos. 58-148502, 59-5704, 5-22213, 7-170548, 8-8814, 9-200115, 9-321517, 10-51380, 9-182148, 10-285092, and 10-313472.